1. Field of the Invention
The present invention relates to a dual-type air conditioning system for vehicles having a front and rear evaporator provided at the front and rear sides of the vehicle. More specifically, the invention relates to a dual-type air conditioning system for vehicles, in which the installation space for a refrigerant discharging pipe installed in the refrigerant discharging sides respectively of the front and rear evaporators can be minimized, and wherein the arrangement of the refrigerant discharging pipe is improved to prevent the refrigerant from back-flowing, thereby facilitating smooth operation of the compressor and improving the performance of the air conditioning system.
2. Background of the Related Art
In the air conditioning system for a vehicle, generally, the compressor driven by the engine power compresses the refrigerant and sends the compressed refrigerant to the condenser. In the condenser, the refrigerant is condensed by a forced blowing of a cooling fan. Then, the refrigerant passes, in sequence, a receiver drier, an expansion valve and an evaporator, and is returned to the compressor. During this course of circulation, the air, which is blown by a blower unit installed in the inlet end of the air conditioning case, is heat-exchanged with the refrigerant passing through the evaporator. The heat-exchanged cooled air is discharged into the occupant compartment of the vehicle to thereby cool the inside room of the car. On the other hand, while the engine coolant is returned to the engine via a heater core, the air blown by a blower unit is heat-exchanged with the coolant passing through the heater core. Then, the heated air is discharged into the occupant compartment of the vehicle to thereby heat the inside room of the car.
In the air conditioning system having the above-described construction, a small car having a small interior space employs a single-type air conditioning system, which is provided with a single evaporator installed in the engine room, i.e., at the front side of the car. In case of luxurious cars or leisure vehicles, a dual-type air conditioning system is applied in order to extend an air conditioning effect up to the rear side of the interior room of the vehicle. The dual-type system comprises a front-seat air conditioning system having an evaporator installed in the engine room and a rear-seat air conditioning system having an evaporator provided at the rear side of the car.
In the dual-type air conditioning system having the front-seat and rear-seat air conditioning systems, the front and rear evaporators can be operated simultaneously or separately. The front and rear evaporators form a refrigerating cycle where the refrigerant is circulated through a single compressor and a single condenser.
FIG. 1 is a drawing of a typical dual-type air conditioning system for a car.
As shown in FIG. 1, a conventional dual-type air conditioning system for a car comprises a compressor 300 for suctioning and compressing the refrigerant and circulating it to the condenser 400. A first and second refrigerant guide pipes 500a and 500b are provided for supplying the heat-exchanged refrigerant in the condenser 400 to a front and rear evaporators (not shown), which are installed respectively in a front seat air conditioning system 100 and a rear seat air conditioning system (not shown). A first refrigerant discharging pipe 600a is provided for connecting the refrigerant discharging side with the refrigerant suction side such that the refrigerant is supplied towards the compressor 300 from the front evaporator and is circulated with oil. In addition, a second refrigerant discharging pipe 600b for connecting the refrigerant discharging side of the rear evaporator and the refrigerant suction side of the compressor 300 is provided such that the refrigerant is supplied towards the compressor 300 from the rear evaporator.
As described above, in the conventional dual-type air conditioning system for a vehicle, when the front and rear evaporators are operated simultaneously, a low-temperature and low-pressure refrigerant discharged from the front and rear evaporators is returned to the compressor. At this time, the compressor is smoothly operated due to the oil mixed in the refrigerant.
When only the front evaporator is operated, however, the refrigerant remains stagnant in the second refrigerant discharging pipe 600b installed in the refrigerant discharging side of the rear evaporator during the course of refrigerant circulation. That is, it occurs when the high-temperature and high-pressure refrigerant discharged from the compressor 300 is returned to the compressor 300 as a low-temperature and low-pressure refrigerant through the front evaporator via the condenser 400. Therefore, a problem occurs in the operation of the compressor owing to the lack of oil in-flown to the compressor 300.
In other words, according to the above conventional refrigerating cycle of a dual-type air conditioning system for a vehicle, a refrigerant joining point S, where the first refrigerant discharging pipe 660a installed in the refrigerant discharging side of the front evaporator is joined with the second refrigerant discharging pipe 600b installed in the refrigerant discharging side of the rear evaporator, is located near the front evaporator. In addition, the second refrigerant discharging pipe 600b is disposed below the refrigerant joining point S. Therefore, a part of the low-temperature and low-pressure refrigerant, which flows into the refrigerant joining point S through the first refrigerant discharging pipe 600a, naturally flows into the second refrigerant discharging pipe 600a, and consequently a certain amount of refrigerant stays inside the second refrigerant discharging pipe 600a. Here, as the operation of the front evaporator continues, the low-temperature and low-pressure refrigerant remains stagnant in the second refrigerant discharging pipe 600b to the level above a certain amount, and the amount of oil mixed in the low-temperature and low pressure refrigerant is increased to the level more than a certain amount. Accordingly, the amount of the oil flowing into the compressor 300 is decreased, and thus the compressor can not be normally operated and also the heat-exchanging performance is deteriorated.
As an attempt in order to solve the above problems, Japanese Laid-open Patent No. 2002-67669 discloses an air conditioning system, in which the compressor can carry out a normal operation when the front evaporator is operated and at the same time the rear evaporator is not operated.
FIG. 2 is a schematic diagram for the refrigerant discharging-pipe in another conventional refrigerating cycle of a dual-type air conditioning system for a vehicle. FIG. 3 shows the conventional refrigerating cycle of FIG. 2, which is installed in a car. Similar to the conventional refrigerating cycle as described above in conjunction with FIG. 1, the conventional refrigerating cycle shown in FIGS. 2 and 3 comprises a compressor 1300 for suctioning and compressing a refrigerant and flowing it to a condenser 1400, a first and second refrigerant guide pipes 1500a and 1500b for supplying the heat-exchanged refrigerant in the condenser 1400 to a front and rear evaporators 1100 and 2100, a first refrigerant discharging pipe 1600a for discharging the refrigerant towards the compressor 1300 from the front evaporator 1500a, and a second refrigerant discharging pipe 1600b for discharging the refrigerant towards the compressor 1300 from the rear evaporator 2100.
The first and second refrigerant guide pipes 1500a and 1500b are branched towards the front and rear evaporators 1100 and 2100. The second refrigerant discharging pipe 1600b is connected at a desired position of the first refrigerant discharging pipe 1600a such that the refrigerant discharged from the first refrigerant discharging pipe 1600a is joined with the refrigerant discharged from the second refrigerant discharging pipe 1600b. 
The second refrigerant discharging pipe 1600b is formed in such a manner that it is protruded upwards from a joining portion J, which is a refrigerant joining point with the first refrigerant discharging pipe 1600a. The second refrigerant discharging pipe 1600b is provided with a first bent portion 1600b-1 180°-bent from the joining portion J, and a descending portion 1600b-2 connected with the first bent portion 1600b-1 and also connected to the refrigerant discharging side of the rear evaporator 2100.
In addition, the first bent portion 1600b-1 is provided with a first bent slant portion 1600b-3 slant-formed in such a way that the joining portion J side is lowered. Also, the first bent portion 1600b-1 is provided with a second bent slant portion 1600b-4 slant-formed in such a way that the descending portion 1600b-2 is lowered.
Furthermore, the second refrigerant discharging pipe 1600b is provided at its lower side with a second bent portion 1600b-5 formed by 360°-bending such that the oil flowing towards the descending portion 1600b-2 is not flown towards the rear evaporator 2100 through the second refrigerant discharging pipe 1600b, even in case where the oil flows towards the descending portion 1600b-2. The height of the first bent portion 1600b-1 of the second refrigerant discharging pipe 1600b, which is connected to the first refrigerant discharging pipe 1600a, is set to be within a range of at least 100˜120 mm.
As described above, the conventional refrigerating cycle of a dual-type air conditioning system for a vehicle is provided with the first bent portion 1600b-1 of the second refrigerant discharging pipe 1600b, which is protruded upwards from the joining portion J of a refrigerant joining point, and the second bent portion 1600b-5 bent more than 360°. Due to the first and second bent portions 1600b-1 and 1600b-5, the refrigerant is prevented from back-flowing towards the rear evaporator 2100 through the second refrigerant discharging pipe 1600b. 
However, the above-described conventional refrigerating cycle of a dual-type air conditioning system for a vehicle is structured similarly to the refrigerant cycle shown in FIG. 1. That is, the joining portion J, which is a refrigerant joining point, is placed near the front evaporator 1100. The first and second refrigerant discharging pipes 1600a and 1600b are connected through the joining portion J, and simultaneously the first bent portion 1600b-1 is erectly installed. In order for the refrigerant to be prevented from back-flowing towards the second refrigerant discharging pipe 1600b, therefore, when the first and second refrigerant discharging pipes 1600a and 1600b are installed, they must comply with the complicated arrangement criteria such as the height and the bending angle of each pipe. In consequence, the installation thereof is restricted due to the limited installation space of the engine room.